Exchange POP3 mailbox access in a front-end/ back-end topology

So you’ve got your nice front-end/back-end topology and you have an application that needs POP3 access to a mailbox. You enable POP3 on the front-end but your application still can’t connect? There seems to be a common misconception (and one that I had when I first started working with Exchange 2000) that in a front-end/back-end environment you only need to enable POP3 on the front-end servers. This isn’t the case. You also need to enable POP3 on any back-end servers that will be hosting the mailboxes that you require access to. This also applies if you are using IMAP4.

Keeping the above in mind the front-end/back-end principle works perfectly. We have several shipping applications that use POP3 to access mailboxes. By pointing them to the network load balanced address of our front-end servers we don’t need to reconfigure the application if we move the mailboxes around. We still have to follow strict change control with any move but it makes our lives and those of the application admins a whole lot easier.

To enable POP3 on a regular back-end mailbox server just enable the Microsoft Exchange POP3 service in the Services MMC console and ensure the POP3 Virtual Server is started in Exchange System Manager. Depending on your policy settings you may also need to enable POP3 on the Exchange Features tab of the user object in Active Directory Users & Computers. However, if the mailbox resides on a cluster server there are a few more steps to follow:

Firstly enable the Microsoft Exchange POP3 service on all nodes. I speak from bitter experience when I say that if you leave it as disabled when you add a POP3 cluster resource the cluster will be unable to bring it online and will try to fail over.

Next you need to add the cluster resource. In Cluster Administrator right click on your cluster group and select New > Resource. Complete the required information making sure you select the correct Resource Type.

On the next screen select the nodes to be the possible owners.

Finally select the Microsoft Exchange System Attendant as a dependency. Once the setup of the resource is complete you should be able to bring it online successfully.